VJC 2023 Intro to org chem notes

VICTORIA JUNIOR COLLEGE CHEMISTRY DEPARTMENT Mrs Mah Ai Ling / poh.ailing@vjc.edu.sg INTRODUCTION TO ORGANIC CHEMISTRY Lecture 1 2 Pages 1 – 11 11 – 19 Complete by T3W6 Tutorial questions 1 – 3 4 – 8 ______________________________________________________________________________ LECTURE OUTLINE 1 What is Organic Chemistry? 2 Formulae of Organic Compounds 3 Common Terminology 4 Hybridisation 5 Shapes of Organic Molecules 6 Types of Organic Reactions 7 Reaction Mechanisms 7.1 Types of Reagents 7.2 Names of Reaction Mechanisms 7.3 Bond Fission (breaking of covalent bonds) 8 Factors Affecting Reactivity of Organic Compounds ASSESSMENT OBJECTIVES Candidates should be able to: (a) interpret, and use the nomenclature, general formulae and displayed formulae of the following classes of compound: (i) hydrocarbons (alkanes, alkenes and arenes) (ii) halogen derivatives (halogenoalkanes and halogenoarenes) (iii) hydroxyl compounds (alcohols and phenols) (iv) carbonyl compounds (aldehydes and ketones) (v) carboxylic acids and derivatives (acyl chlorides and esters) (vi) nitrogen compounds (amines, amides, amino acids and nitriles) (b) interpret, and use the following terminology associated with organic reactions: (i) functional group (ii) degree of substitution: primary, secondary, tertiary, quaternary (iii) homolytic and heterolytic fission (iv) carbocation (v) free radical, initiation, propagation, termination (vi) electrophile (Lewis acid), nucleophile (Lewis base) (vii) addition, substitution, elimination, condensation, hydrolysis (viii) oxidation and reduction [in equations for organic redox reactions, the symbols [O] and [H] are acceptable] (c) interpret, and use the following terminology associated with organic reactivities: (i) delocalisation (ii) electronic effect (electron-donating and electron-withdrawing effect) (iii) steric effect (steric hindrance) (d) describe sp 3 hybridisation, as in ethane molecule, sp 2 hybridisation, as in ethene and benzene molecules, and sp hybridisation, as in ethyne molecule (e) explain the shapes of, and bond angles in, the ethane, ethene, benzene, and ethyne molecules in relation to  and  carbon-carbon bonds (f) predict the shapes of, and bond angles in, molecules analogous to those specified in (e) (g) apply (b) and (c) to the understanding of mechanisms in terms of organic structure and bonding (h) recognise that the mechanisms of polar reactions involve the flow of electrons from electron -rich to electron-poor sites

2 INTRODUCTION TO ORGANIC CHEMISTRY 1 What is Organic Chemistry? • It is the study of th e chemistry of carbon compounds other than its oxides, metallic carbonates and related compounds. • More than 6 million organic compounds have been identified. This ability of carbon to form so many stable compounds is because (i) strong bonds can be formed between two carbon atoms, e.g. C –C bond is much stronger compared to single bonds formed between atoms of other elements. This allows carbon to form long chains (catenation) and rings, resulting in a wide variety of possible molecules. bond energy / kJ mol–1 C–C 350 N–N 160 O–O 150 (ii) carbon is tetravalent, which allows branching of carbon chains into side chains and formation of double or triple bonds, further increasing the number of carbon compounds which can be formed. (iii) carbon forms strong covalent bonds with other elements, e .g. H, N, O, S and the halogens. 2 Formulae of Organic Compounds • Empirical formula shows the simplest ratio of the atoms of the different elements present in the compound. E.g. C2H4O • Molecular formula shows the actual number of atoms of each element present in one molecule of the compound. E.g. C4H8O2 • Constitutional formula (structural formula) shows how the constituent atoms of a molecule are joined together. E.g. CH3CH2CH2CO2H and (CH3)2CHCO2H have different structural formulae but the same molecular formula of C4H8O2. • Displayed formula or full s tructural formula is the detailed structure of a molecule showing the arrangement of the atoms and all the bonds between them. E.g.

3 • Skeletal formula shows the carbon skeleton of the molecule without showing the carbon atoms and the C –H bonds and atoms in the molecule. Only the carbon –carbon bonds, bonds to functional groups and functional groups are shown. E.g. CH3CH2CH2CO2H (CH3)2CHCO2H • Stereochemical formula shows the spatial arrangement of the bonds, atoms and groups in a molecule as a perspective 3-dimensional formula. E.g. OR Making Thinking Visible Question: What are the possible types of carbon-carbon bonds? Answer: C–C, C=C, C≡C, (benzene) Question: What does a normal straight line, a solid wedge and a dashed wedge represent in the stereochemical formula? Answer: Normal straight line: bond lies on the plane of the paper Solid wedge: bond pointing out of the plane of the paper Dashed wedge: bond pointing into the plane of the paper 3 Common Terminology • Hydrocarbons are compounds containing carbon and hydrogen only. The simplest hydrocarbons, containing only single bonds are the alkanes with general formula CnH2n+2. E.g. molecular formula structural formula name CH4 CH4 methane C2H6 CH3CH3 ethane C3H8 CH3CH2CH3 propane C4H10 CH3(CH2)2CH3 butane C5H12 CH3(CH2)3CH3 pentane • Alkyl group is a group of carbon and hydrogen having the general formula CnH2n+1. It is usually denoted by the letter R. The name follows that of corresponding al kane but with the suffix –yl instead of –ane. E.g. alkyl group name alkyl group name CH3– methyl CH3(CH2)2CH2– butyl CH3CH2– ethyl CH3(CH2)3CH2– pentyl CH3CH2CH2– propyl

4 Candidates should be able to: (b) interpret, and use the following terminology associated with organic reactions: (i) functional group • Functional group consists of an element (e.g. –Br) or combination of elements (e.g. –OH, –CO2H) responsible for the chemical reactions of an organic compound. • Homologous series is a family of compounds containing the same functional group but differing by a common increment of a –CH2– group between one member and the next. All compounds in any one homologous series (i) undergo similar chemical reactions (due to presence of the same functional group). (ii) can be prepared by similar methods. (iii) have a relative molecular mass 14 units greater than the preceding compound in the series (due to the presence of an additional –CH2– group). (iv) exhibit a regular gradation of physical properties (due to the increasing size of hydrocarbon chain). Candidates should be able to: (a) interpret, and use the nomenclature, general formulae and displayed formulae of the following classes of compound: (i) hydrocarbons (alkanes, alkenes and arenes) (ii) halogen derivatives (halogenoalkanes and halogenoarenes) (iii) hydroxyl compounds (alcohols and phenols) (iv) carbonyl compounds (aldehydes and ketones) (v) carboxylic acids and derivatives (acyl chlorides and esters) (vi) nitrogen compounds (amines, amides, amino acids and nitriles) class / name of functional group * not regarded as functional group general formula structure of functional group hydrocarbons *alkanes RH or CnH2n+2 – alkenes CnH2n alkynes (not in syllabus) CnH2n–2 −CC− *arenes (contain benzene ring, ) – – (Note: The benzene ring is regarded as forming part of the hydrocarbon chain and is hence usually not classified as a functional group.) halogen derivatives halogenoalkanes RX (X= Cl, Br, I) –X halogenoarenes (X= Cl, Br, I) –X

5 class / name of functional group general formula structure of functional group hydroxyl compounds and derivatives alcohols ROH –OH phenols –OH ethers (not in syllabus) ROR’ –O– carbonyl compounds aldehydes *R